Hypereutectic Al-Mg2Si composite material and preparation method thereof

Abstract

The hypereutectic Al-Mg2Si composite material is prepared from the following components in percentage by mass: 9.0 to 22.1 percent of Mg, 6.5 to 16.0 percent of Si, 0 to 0.8 percent of Cu, 0.1 to 0.8 percent of Fe, 0 to 0.4 percent of Mn, 0.002 to 0.005 percent of Be, 0.006 to 0.05 percent of Sr, 0.10 to 0.20 percent of RE, less than or equal to 0.15 percent of trace impurities and the balance of Al, the mass ratio of Mg to Si is less than or equal to 1.7, and RE is selected from at least one of La and Ce. The hypereutectic Al-Mg2Si composite material disclosed by the invention has relatively fine primary Mg2Si and eutectic Mg2Si, the optimized microstructure can obviously improve the strength and plasticity of the composite material, and the hypereutectic Al-Mg2Si composite material has relatively high obdurability.

Description

Technical Field

[0001] The invention belongs to the field of alloys, and in particular relates to a hypereutectic Al-Mg2Si composite material and a preparation method thereof. Background Art

[0002] Mg2Si has the advantages of high melting point, high hardness, high elastic modulus, low density and low thermal expansion coefficient, and can be formed in situ. It is one of the ideal reinforcing phases for preparing lightweight and high-strength aluminum matrix composites. However, the primary Mg2Si formed in the hypereutectic Al-Mg2Si composites prepared by traditional casting process is coarse fishbone, dendrite and dendrite, which seriously splits the matrix and significantly affects the mechanical properties of the material. In addition, the eutectic Mg2Si phase is in the form of network flakes, which also has an adverse effect on the performance of the alloy. Therefore, how to regulate the morphology, size and distribution of primary and eutectic Mg2Si particles has become one of the keys to preparing lightweight and high-strength Al-Mg2Si composites.

[0003] In recent years, domestic and foreign scholars have conducted a lot of research on the modification of Mg2Si phase in Al-Mg2Si composite materials. The study found that when the Ce addition amount was 0.6%, the tensile strength and elongation of the hypereutectic Al-Mg2Si alloy increased by 30% and 70% respectively. Subsequent elements such as Li, Sb, P, Sc, Er, and Bi also had a significant modification effect on primary Mg2Si, but there were fewer modification elements for eutectic Mg2Si. CN109777986A proposed a preparation and organization optimization method for in-situ generated Mg2Si particle reinforced aluminum-based composite materials by adding 0.05-0.5% Sr, 0.05-1% P and 0.05-0.5% Ti. Through the adsorption and poisoning effect of Sr primary Mg2Si phase and eutectic Si, the nucleation inhibition effect of AlP on Mg2Si, and the grain refinement effect of Al3Ti, the synergistic refinement of multiple alloy structures is achieved, thereby improving the performance of the alloy. CN105063393A discloses a Mg2Si / Al-based composite material and a composite optimization method thereof, wherein a copper-phosphorus master alloy is added to the molten Mg2Si / Al-based composite material to provide a large number of cores for the nucleation of primary Mg2Si, significantly refine the primary Mg2Si, and improve the mechanical properties of the composite material. CN1472355A discloses a Sr-Ce composite refinement treatment process for a hypereutectic Al-Mg2Si-Si alloy, wherein by respectively adding Al-Sr with a Sr content of 0.1 to 1.3% and Al-Ce with a Ce content of 0.6 to 0.8%, the Mg2Si reinforced particles are significantly refined, and the particle size is reduced to below 15 μm, so that the material is more suitable for the application field of particle-reinforced metal-based composite materials. In addition, CN109112368A and CN111118355A respectively provide a rare earth modification method, by adding 0.15-0.35% Sc and 0.1-0.3% Er, thereby improving the morphology of the eutectic Mg2Si phase and improving the strength and plasticity of the alloy.

[0004] In summary, the current modification methods for the Mg2Si phase in hypereutectic Al-Mg2Si alloys are mainly divided into two categories. P, Sb, Bi, etc. are used for the modification of primary Mg2Si, while Sc and Er can be used for the modification of eutectic Mg2Si. However, there are few methods for simultaneously achieving the modification of primary and eutectic Mg2Si. Summary of the invention

[0005] In order to overcome the problems existing in the prior art, one of the objectives of the present invention is to provide a hypereutectic Al-Mg2Si composite material.

[0006] A second object of the present invention is to provide a method for preparing the above-mentioned hypereutectic Al-Mg2Si composite material.

[0007] A third object of the present invention is to provide the application of the above-mentioned hypereutectic Al-Mg2Si composite material and its preparation method in the fields of automobiles, communications, electronics or aerospace.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] The first aspect of the present invention provides a hypereutectic Al-Mg2Si composite material, which is composed of the following components in mass percentage: Mg 9.0-22.1%, Si 6.5-16.0%, Cu 0-0.8%, Fe 0.1-0.8%, Mn 0-0.4%, Be 0.002-0.005%, Sr 0.006-0.05%, RE 0.10-0.20%, trace impurities ≤0.15%, Al as the balance,

[0010] Wherein, the mass ratio of Mg to Si is ≤1.6, and RE is selected from at least one of La and Ce;

[0011] The hypereutectic Al-Mg2Si composite material contains Mg2Si.

[0012] In the present invention, the mass percentage of Mg is 9-22.1%, for example, it can be selected from 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 22.1%. In the present invention, the mass percentage of Mg exceeds 8.8%, that is, the content of Mg and Si exceeds the eutectic point, and the Mg / Si ratio is not higher than 1.7, which ensures the formation of primary Mg2Si. At the same time, there is a part of residual Si element in the hypereutectic Al-Mg2Si composite material, which is beneficial to improve the fluidity of the hypereutectic Al-Mg2Si composite material.

[0013] In the present invention, the mass percentage of Si is 6.5-16.0%, for example, can be selected from 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%.

[0014] In the present invention, the mass percentage of Cu is 0-0.8%, for example, it can be selected from 0%, 01%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%. The role of Cu in the present invention is to improve the strength of the hypereutectic Al-Mg2Si composite material, but the content of Cu cannot be higher than 0.8%, otherwise it will affect the fluidity and liquidus of the hypereutectic Al-Mg2Si composite material.

[0015] In the present invention, the mass percentage of Fe is 0.1-0.8%, for example, it can be selected from 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%. The Fe in the present invention is derived from the preparation of raw aluminum recycling materials. In order to improve the recycling efficiency of recycled aluminum, the tolerance of the Fe element in the hypereutectic Al-Mg2Si composite material is greatly increased to 0.8%, that is, no additional Fe is added, and the original Fe content of the original aluminum recycling material is maintained.

[0016] In the present invention, the mass percentage of Mn is 0-0.4%, for example, it can be selected from 0%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, and 0.4%.

[0017] In the present invention, the mass percentage of Be is 0.002-0.005%, for example, it can be selected from 0.002%, 0.0025%, 0.003%, 0.0035%, 0.004%, 0.0045%, 0.005%. In the present invention, the Be element can reduce the burning loss of Mg, Sr and RE in the smelting process, and at the same time change the type of the iron-rich phase, promote the beneficial transformation of the iron-rich phase, and thus increase the allowable Fe content in the hypereutectic Al-Mg2Si composite material.

[0018] In the present invention, the mass percentage of Sr is 0.006-0.05%, for example, can be selected from 0.006%, 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%.

[0019] Preferably, the Sr is added in the form of Al-Sr-RE alloy.

[0020] Preferably, the RE is added in the form of RE, Al-RE, or Al-Sr-RE alloy.

[0021] The present invention modifies primary Mg2Si and eutectic Mg2Si by adding RE and a trace amount of Al-Sr-RE master alloy. The principle of RE modifying primary Mg2Si is that rare earth elements such as Ce and La have a high solid solubility in Mg2Si, but the solid solution of RE atoms causes a certain lattice distortion of Mg2Si, that is, the surface energy of the Mg2Si crystal is changed, and the anisotropic growth of the Mg2Si crystal is inhibited, thereby obtaining fine and dense polygonal primary Mg2Si. The principle of Al-Sr-RE modifying eutectic Mg2Si is that Al-Sr-RE contains Al4 (SrRE) and Al doped with Sr and RE. 11(SrRE)3, these two phases have high formation temperature and high chemical activity, and are easily aggregated at the solid-liquid interface of the eutectic Mg2Si phase, inhibiting the lateral growth of the eutectic Mg2Si and promoting its twinning transformation, ultimately obtaining fine whisker-like and granular Mg2Si, which significantly improves the plasticity of the hypereutectic Al-Mg2Si composite material.

[0022] In the present invention, the mass percentage of RE is 0.10-0.20%, for example, can be selected from 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%.

[0023] Preferably, the average equivalent circular diameter of the primary Mg2Si is not higher than 15 μm, and the average equivalent circular diameter of the eutectic Mg2Si is not higher than 3 μm.

[0024] Preferably, taking the total mass percentage of the hypereutectic Al-Mg2Si composite material as 100%, the mass percentage of the Mg2Si is greater than 13.9%. For example, the mass percentage of Mg2Si can be selected from 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 24%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, etc. According to the binary phase diagram of Al-Mg2Si, the eutectic point of Al-Mg2Si is 13.9%. When the mass fraction of Mg2Si is higher than this value, it is called a hypereutectic alloy, and the structure contains a primary phase and a eutectic phase. On the contrary, when the mass fraction of Mg2Si does not exceed this value, it is a hypoeutectic or eutectic alloy, and only a eutectic phase exists.

[0025] Preferably, when the mass percentage of Fe in the hypereutectic Al-Mg2Si composite material is 0.2-0.6%, the mass percentage of Mn is not 0. When the Fe content is 0.2-0.6%, the corresponding Mn addition amount can be calculated by thermodynamic calculation according to the subsequent casting method and use of the hypereutectic Al-Mg2Si composite material. If used for casting, especially die casting, it is necessary to add a considerable amount of Mn to the Fe alloy to determine that the formation temperature of the Al(FeMn)Si quaternary phase is close to the Mg2Si eutectic temperature to obtain a ternary eutectic structure, reduce the harm of the Fe phase, and improve the stickiness of the alloy during casting, thereby broadening the application of the alloy. For semi-continuous cast rods used for deformation processing, the low Fe can be retained without adding the Mn element.

[0026] The second aspect of the present invention provides a method for preparing the hypereutectic Al-Mg2Si composite material according to the first aspect of the present invention, comprising the following steps:

[0027] S1: melting part of the raw materials and performing the first refining, and then adding Al-Be alloy to obtain the first melt;

[0028] S2: melting the first melt, Mg, optionally added Mn, and RE, and then performing a second refining to obtain a second melt;

[0029] S3: melting the second melt and the Al-Sr-RE alloy, and then casting to obtain the hypereutectic Al-Mg2Si composite material.

[0030] The present invention adds RE in step S2, utilizes RE to modify the primary Mg2Si in the hypereutectic Al-Mg2Si composite material, adds Al-Sr-RE alloy to modify the eutectic Mg2Si in step S3, refines the Mg2Si by synergistically modifying the primary and eutectic Mg2Si, and improves the microstructure and performance of the alloy. The mass percentage of Mg2Si in the present invention is greater than 13.9%, which is a hypereutectic, and a rare earth modification step needs to be added, that is, RE is added in step S2 to modify the primary Mg2Si. The principle is that rare earth elements such as Ce and La have a high solid solubility in Mg2Si, but the solid solution of RE atoms causes a certain lattice distortion of Mg2Si, that is, the surface energy of the Mg2Si crystal is changed, and the anisotropic growth of the Mg2Si crystal is inhibited, thereby obtaining a small and dense polygonal primary Mg2Si.

[0031] In the present invention, fusion refers to the melting and integration of two or more solid metals or alloys.

[0032] Preferably, the step S2 further comprises the step of adding raw materials until the alloy composition reaches a qualified level; the step of adding raw materials until the alloy composition reaches a qualified level is located before and / or after the smelting step.

[0033] Preferably, based on the mass percentage of the Al-Sr-RE alloy being 100%, the total mass percentage of Sr and RE is 15-23%.

[0034] Preferably, based on the mass percentage of the first melt being 100%, the mass percentage of the RE is 0.06% to 0.18%.

[0035] Preferably, based on the mass percentage of the second melt being 100%, the mass percentage of the Al—Sr—RE alloy is 0.1% to 1.0%.

[0036] Preferably, the first refining step is: refining by introducing a halide salt refining agent using an inert gas as a carrier; further preferably, the first refining step is: refining by introducing a halide salt refining agent using nitrogen as a carrier.

[0037] Preferably, the halide salt refining agent contains NaCl, KCl, and Na3AlF.

[0038] Preferably, the second refining step is: refining by passing a sodium-free halide salt refining agent using an inert gas as a carrier; further preferably, the second refining step is: refining by passing a sodium-free halide salt refining agent using argon as a carrier. When refining the melt after adding Mg, a sodium-free refining agent is used to eliminate the adverse effects of Na on the high-Mg melt.

[0039] Preferably, the sodium-free halide salt refining agent contains MgCl2, KCl, and K3AlF6.

[0040] Preferably, the inert gas is selected from at least one of nitrogen, argon and xenon.

[0041] Preferably, some of the raw materials include recycled aluminum; further preferably, some of the raw materials include at least one of Al-Si-Mg recycled aluminum, Al-Si-Mg-Cu recycled aluminum, Al-Mg-Si recycled aluminum, and Al-Mg-Si-Cu recycled aluminum; further preferably, the raw materials in the step include at least one selected from Al-Si-Mg recycled aluminum, Al-Si-Mg-Cu recycled aluminum, Al-Mg-Si recycled aluminum, and Al-Mg-Si-Cu recycled aluminum, aluminum ingots, silicon, and copper. The present invention uses at least one of Al-Si-Mg recycled aluminum, Al-Si-Mg-Cu recycled aluminum, Al-Mg-Si recycled aluminum, and Al-Mg-Si-Cu recycled aluminum as the main raw material, and prepares the target alloy composition by adding aluminum ingots, silicon, copper ingots, magnesium ingots, manganese ingots, Al-Be, Al-Sr-RE, and RE in appropriate amounts. Fe is an impurity component in the recycled aluminum and is not added additionally. The content of Mn is added according to the content of Fe and the composition requirements.

[0042] Preferably, the melting temperature in step S1 is 770-850°C.

[0043] Preferably, the casting step is: removing scum on the surface of the melt, introducing the melt into a flow channel, and after rotary degassing and double-layer filtration, casting and forming in a heat-insulating furnace.

[0044] The third aspect of the present invention provides the application of the hypereutectic Al-Mg2Si composite material described in the first aspect of the present invention and / or the method for preparing the hypereutectic Al-Mg2Si composite material described in the second aspect of the present invention in the automotive, communication, electronics or aerospace fields.

[0045] The beneficial effects of the present invention are: the hypereutectic Al-Mg2Si composite material in the present invention has relatively fine primary Mg2Si and eutectic Mg2Si, and the optimized micromorphology can significantly improve the strength and plasticity of the hypereutectic Al-Mg2Si composite material, and has high toughness, which can meet the performance requirements of the hypereutectic Al-Mg2Si composite material in the fields of automobiles, communications, electronics, aerospace, etc. The performance that the hypereutectic Al-Mg2Si composite material in the present invention can achieve is specifically: in the gravity casting state, the tensile strength is 185-200MPa, the yield strength is 105-110MPa, and the elongation reaches 6-8%; in the T6 state, the tensile strength is 300-360MPa, the yield strength is 235-270MPa, and the elongation reaches 5-7%.

[0046] The preparation method of the present invention is simple and easy to operate. The primary Mg2Si is modified by RE, and the eutectic Mg2Si is modified by Al-Sr-RE. After the synergistic modification by RE and Al-Sr-RE, the Mg2Si can be significantly refined, the microstructure of the hypereutectic Al-Mg2Si composite material is improved, and the strength and plasticity of the prepared hypereutectic Al-Mg2Si composite material are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is the metallographic image of the hypereutectic Al-Mg2Si composite material in Example 1 at a scale of 500 μm.

[0048] Figure 2 This is the metallographic image of the hypereutectic Al-Mg2Si composite material in Example 2 at a scale of 500 μm.

[0049] Figure 3 This is the metallographic image of the hypereutectic Al-Mg2Si composite material in Example 1 when the scale is 20 μm.

[0050] Figure 4 This is the metallographic image of the hypereutectic Al-Mg2Si composite material in Example 2 when the scale is 20 μm.

[0051] Figure 5 This is the XRD diagram of the hypereutectic Al-Mg2Si composite material in Example 1. DETAILED DESCRIPTION

[0052] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that if there are processes that are not particularly described in detail below, they can be implemented or understood by those skilled in the art with reference to the prior art. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be purchased commercially.

[0053] Example 1

[0054] This example provides a hypereutectic Al-Mg2Si composite material, which is composed of the following components in mass percentage: Mg 10.0%, Si 6.5%, Cu 0.4%, Fe 0.1%, Be 0.003%, Sr 0.006%, Ce 0.1%, and the balance is Al and inevitable trace impurities.

[0055] The hypereutectic Al-Mg2Si composite material in this example is prepared by a preparation method comprising the following steps:

[0056] (1) Ingredients: The amount of each raw material is calculated according to the component composition of the hypereutectic Al-Mg2Si composite material in this example, wherein Al-Si-Mg-(Cu) and Al-Mg-Si-(Cu) series recycled aluminum are used as the main raw materials, and the target alloy composition is prepared by adding appropriate amounts of aluminum ingots, magnesium ingots, Si, Cu, Al-Be and Al-Sr-RE master alloys. Fe is used as an impurity element and is not added additionally.

[0057] (2) Melting: Most of the recycled aluminum, aluminum ingots, Si and Cu and other raw materials that are not easy to burn are added into the melting furnace and then heated to 800℃ for melting.

[0058] (3) Refining: Add the remaining recycled aluminum and adjust the melt temperature to 750°C; use 99.9% nitrogen as a carrier, introduce a halide salt refining agent (commercially available product, the main components are NaCl, KCl, Na3AlF) accounting for 0.1% of the melt mass, and turn on the electromagnetic stirring system for 5 minutes; then add Al-Be master alloy with a Be content of 0.003%;

[0059] (4) Composition adjustment: remove the surface scum, take samples to test the composition, and according to the test results, replenish the raw materials and add Mg ingots and 0.06% Ce rare earth by mass of the melt; turn on the electromagnetic stirring system for 3 minutes; test the alloy composition for the second time and adjust the alloy composition to meet the requirements.

[0060] (6) Refining: Using 99.9% high-purity argon as a carrier, 0.1% of the melt mass is introduced into a Na-free halide salt refining agent (commercially available product, the main components of which are MgCl2, KCl, and K3AlF6);

[0061] (7) Composite modification: add 0.1% Al-8Sr-8Ce composite modifier (the total mass percentage of the composite modifier is 100%, the mass percentage of Sr is 8%, and the mass percentage of Ce is 8%) to the melt, turn on the electromagnetic stirring system for 2 minutes, and then keep it warm and let it stand;

[0062] (8) Casting: The scum on the surface of the melt is removed, and the melt is introduced into a flow channel. After rotary degassing and double-layer filtration, the melt is introduced into a semi-continuous casting device to prepare a cast rod, which is the hypereutectic Al-Mg2Si composite material in this example.

[0063] Example 2

[0064] This example provides a hypereutectic Al-Mg2Si composite material, which is composed of the following components in mass percentage: Mg 12.65%, Si 9.5%, Cu 0.1%, Fe 0.5%, Mn 0.3%, Be 0.005%, Sr 0.02%, RE 0.15%, and the balance is Al and inevitable trace impurities.

[0065] The hypereutectic Al-Mg2Si composite material in this example is prepared by a preparation method comprising the following steps:

[0066] (1) Ingredients: The amount of each raw material is calculated according to the component composition of the hypereutectic Al-Mg2Si composite material in this example, wherein Al-Si-Mg-(Cu) and Al-Mg-Si-(Cu) series recycled aluminum are used as the main raw materials, and the target alloy composition is prepared by adding appropriate amounts of aluminum ingots, magnesium ingots, Si, Mn agent, Cu, Al-Be and Al-Sr-RE master alloy. Fe is an impurity element and is not added additionally. The content of Mn is designed according to the content of Fe and the composition requirements.

[0067] (2) Melting: Most of the recycled aluminum, aluminum ingots, Si and Cu and other raw materials that are not easy to burn are added into the melting furnace, and then the temperature is raised to 850℃ for melting.

[0068] (3) Refining: Add the remaining recycled aluminum and adjust the melt temperature to 770°C; use 99.9% nitrogen as a carrier, introduce 0.1% of the melt mass of a halide salt refining agent (commercially available products, the main components are NaCl, KCl, Na3AlF), and start the electromagnetic stirring system for 6 minutes; then add an Al-Be master alloy with a Be content of 0.005%;

[0069] (4) Composition adjustment: remove the surface scum, take samples to test the composition, and according to the test results, add raw materials and add Mg ingots and 0.1% Ce rare earth by mass of the melt; turn on the electromagnetic stirring system for 5 minutes; test the alloy composition for the second time and adjust the alloy composition to meet the requirements.

[0070] (6) Refining: Using 99.9% high-purity argon as a carrier, 0.1% of the melt mass is introduced into a Na-free halide salt refining agent (commercially available product, the main components of which are MgCl2, KCl, and K3AlF6);

[0071] (7) Composite modification: add 0.5% Al-6Sr-10La composite modifier to the melt (the total mass percentage of the composite modifier is 100%, the mass percentage of Sr is 6%, and the mass percentage of La is 10%), turn on the electromagnetic stirring system for 4 minutes, and then keep it warm and let it stand;

[0072] (8) Casting: The scum on the surface of the melt is removed, and the melt is introduced into a flow channel. After rotary degassing and double-layer filtration, the melt is introduced into a holding furnace and directly supplied to a casting device to obtain the hypereutectic Al-Mg2Si composite material in this example.

[0073] Example 3

[0074] This example provides a hypereutectic Al-Mg2Si composite material, which is composed of the following components in mass percentage: Mg 15.8%, Si 11.5%, Cu 0.2%, Fe 0.8%, Be 0.005%, Sr 0.05%, RE 0.20%, and the balance is Al and inevitable trace impurities.

[0075] The hypereutectic Al-Mg2Si composite material in this example is prepared by a preparation method comprising the following steps:

[0076] (1) Ingredients: The amount of each raw material is calculated according to the component composition of the hypereutectic Al-Mg2Si composite material in this example, wherein Al-Si-Mg-(Cu) and Al-Mg-Si-(Cu) series recycled aluminum are used as the main raw materials, and the target alloy composition is prepared by adding appropriate amounts of aluminum ingots, magnesium ingots, Si, Cu, Al-Be and Al-Sr-RE master alloys. Fe is used as an impurity element and is not added additionally.

[0077] (2) Melting: Most of the recycled aluminum, aluminum ingots, Si and Cu and other raw materials that are not easy to burn are added into the melting furnace, and then the temperature is raised to 860℃ to melt.

[0078] (3) Refining: Add the remaining recycled aluminum and adjust the melt temperature to 770°C; use 99.9% nitrogen as a carrier, introduce a halide salt refining agent (commercially available product, the main components are NaCl, KCl, Na3AlF) accounting for 0.1% of the melt mass, and turn on the electromagnetic stirring system for 8 minutes; then add Al-Be master alloy with a Be content of 0.005%;

[0079] (4) Composition adjustment: remove the surface scum, take samples to test the composition, and according to the test results, add raw materials and add Mg ingots and 0.12% Ce rare earth by mass of the melt; turn on the electromagnetic stirring system for 6 minutes; test the alloy composition for the second time and adjust the alloy composition to meet the requirements.

[0080] (6) Refining: Using 99.9% high-purity argon as a carrier, 0.1% of the melt mass is introduced into a Na-free halide salt refining agent (commercially available product, the main components of which are MgCl2, KCl, and K3AlF6);

[0081] (7) Composite modification: Add 1.0% Al-8Sr-6Ce-2La composite modifier (the mass percentage of Sr is 8%, the mass percentage of Ce is 6%, and the mass percentage of La is 2%, based on the mass percentage of the composite modifier as 100%), turn on the electromagnetic stirring system for 2 minutes, and then keep it warm and let it stand;

[0082] (8) Casting: The scum on the surface of the melt is removed, and the melt is introduced into a flow channel. After rotary degassing and double-layer filtration, the melt is introduced into a holding furnace and directly supplied to a casting equipment for casting to obtain the hypereutectic Al-Mg2Si composite material in this example.

[0083] Example 4

[0084] This example provides a hypereutectic Al-Mg2Si composite material, which is composed of the following components in percentage by mass: Mg 10%, Si 7.5%, Cu 1.0%, Fe 0.6%, Mn 0.25%, Be 0.002%, Sr 0.03%, RE 0.12%, and the balance is Al and inevitable trace impurities.

[0085] The hypereutectic Al-Mg2Si composite material in this example is prepared by a preparation method comprising the following steps:

[0086] (1) Ingredients: The amount of each raw material is calculated according to the component composition of the hypereutectic Al-Mg2Si composite material in this example, wherein Al-Si-Mg-(Cu) and Al-Mg-Si-(Cu) series recycled aluminum are used as the main raw materials, and the target alloy composition is prepared by adding appropriate amounts of aluminum ingots, magnesium ingots, Si, Mn agent, Cu, Al-Be and Al-Sr-RE master alloy. Fe is an impurity element and is not added additionally. The content of Mn is designed according to the content of Fe and the composition requirements.

[0087] (2) Melting: Most of the recycled aluminum, aluminum ingots, Si and Cu and other raw materials that are not easy to burn are added into the melting furnace, and then the temperature is raised to 820℃ to melt.

[0088] (3) Refining: Add the remaining recycled aluminum and adjust the melt temperature to 740°C; use 99.9% nitrogen as a carrier, introduce 0.1% of the melt mass of a halide salt refining agent (commercially available products, the main components are NaCl, KCl, Na3AlF), and start the electromagnetic stirring system for 4 minutes; then add Al-Be master alloy with a Be content of 0.002%;

[0089] (4) Composition adjustment: remove the surface scum, take samples to test the composition, and according to the test results, add raw materials and add Mg ingots and 0.1% Ce rare earth by mass of the melt, and turn on the electromagnetic stirring system for 4 minutes; test the alloy composition for the second time and adjust the alloy composition to meet the requirements.

[0090] (6) Refining: Using 99.9% high-purity argon as a carrier, 0.1% of the melt mass of a Na-free halide salt refining agent (commercially available product, the main components are MgCl2, KCl, K3AlF6) is introduced;

[0091] (7) Composite modification: Add 0.4% Al-10Sr-6La composite modifier (the mass percentage of Sr is 6% and the mass percentage of La is 6% based on the mass percentage of the composite modifier as 100%) to the melt, turn on the electromagnetic stirring system for 2 min, and then keep it warm and let it stand;

[0092] (8) Casting: The scum on the surface of the melt is removed, and the melt is introduced into a flow channel. After rotary degassing and double-layer filtration, the melt is introduced into a holding furnace and directly supplied to a casting device to obtain the hypereutectic Al-Mg2Si composite material in this example.

[0093] Comparative Example 1

[0094] The method for preparing the hypereutectic Al-Mg2Si composite material in this example is different from that in Example 1 in that no Ce rare earth is added in step (4) of this example.

[0095] Comparative Example 2

[0096] The method for preparing the hypereutectic Al-Mg2Si composite material in this example is different from that in Example 1 in that: in step (7) of this example, no Al-Sr-Ce composite modifier is added.

[0097] Comparative Example 3

[0098] The difference between the preparation method of the hypereutectic Al-Mg2Si composite material in this example and that in Example 1 is that an equal amount of Al-Sr is used in step (7) of this example to replace the Al-Sr-Ce composite modifier in Example 1.

[0099] Comparative Example 4

[0100] The difference between the preparation method of the hypereutectic Al-Mg2Si composite material in this example and that in Example 1 is that in step (7) of this example, an equal amount of Al-Ce is used to replace the Al-Sr-Ce composite modifier in Example 1, and the Ce content in Al-Ce is 0.02%.

[0101] Performance Test:

[0102] The metallographic images of the hypereutectic Al-Mg2Si composite materials in Examples 1 and 2 were tested respectively. Figure 1 to Figure 4 As shown by Figure 1 to Figure 4 It can be seen that the primary Mg2Si particle size and distribution in the hypereutectic Al-Mg2Si composite materials of Examples 1 to 2 are uniform, there is no aggregation phenomenon, and the Mg2Si morphology can be significantly improved.

[0103] The XRD data of the hypereutectic Al-Mg2Si composite material in Example 1 was tested by an X-ray diffractometer. The specific test results are as follows: Figure 5 As shown by Figure 5 It can be seen that in the hypereutectic Al-Mg2Si composite material in Example 1, Mg and Si react in situ to generate Mg2Si.

[0104] The hypereutectic Al-Mg2Si composite materials in Examples 1-4 and Comparative Examples 1-4 were subjected to gravity casting and T6 heat treatment, respectively. The T6 heat treatment process was: 535±5°C, heat preservation for 6 hours, water quenching and heating to 175°C, and heat preservation for 8 hours. The tensile test was carried out according to the method listed in the national standard GB / T228.1-2021 "Metallic Material Tensile Test Part 1: Room Temperature Test Method", and the test results are listed in Table 1.

[0105] Table 1 Mechanical properties of alloys in different embodiments and comparative examples

[0106]

[0107] As shown in Table 1, compared with Comparative Examples 1 to 4, the hypereutectic Al-Mg2Si composite materials in Examples 1 to 4 are treated by the preparation method of the present invention, and the plasticity of the materials is significantly improved. The strength of the gravity casting state is improved to a small extent, while the strength of the T6 state is significantly improved, which further shows that for the hypereutectic Al-Mg2Si composite materials, the morphology adjustment of the eutectic Mg2Si and the primary Mg2Si has a great influence on the improvement of the plasticity of the materials. Compared with Comparative Examples 1 and 2, Example 1 is treated by Ce and Al-Sr-Ce composite modifiers, and its cast elongation is increased by about 60.0% and 77.8%; compared with Comparative Examples 3 and 4, Example 1 is treated by Ce and Al-Sr-Ce composite modifiers, and the elongation of the alloy is increased by 45.5%. However, Comparative Example 4 reduces the content of RE, the modification effect of the primary Mg2Si in the alloy is weakened, and the elongation is reduced by 33.3%.

[0108] The average equivalent circle diameters of primary Mg2Si and eutectic Mg2Si of the hypereutectic Al-Mg2Si composite materials of Examples 1 to 4 and Comparative Examples 1 to 3 were tested respectively. Image processing software was used to test and analyze Mg2Si in 5 to 30 50 to 500 times magnification metallographic photographs. The statistically measured average equivalent circle diameter data are shown in Table 2 below.

[0109] Table 2 Average equivalent circle diameter of primary Mg2Si and eutectic Mg2Si

[0110]

[0111]

[0112] It can be seen from Table 2 that compared with comparative examples 1 to 3, the sizes of primary Mg2Si and eutectic Mg2Si in the hypereutectic Al-Mg2Si composite materials of embodiments 1 to 4 are significantly refined, wherein the average equivalent circular diameter of primary Mg2Si in the hypereutectic Al-Mg2Si composite materials of embodiments 1 to 4 is less than 15 μm, and the average equivalent circular diameter of eutectic Mg2Si is less than 3 μm.

[0113] In summary, the hypereutectic Al-Mg2Si composite material in the present invention has relatively fine primary Mg2Si and eutectic Mg2Si, and the optimized micromorphology can significantly improve the strength and plasticity of the hypereutectic Al-Mg2Si composite material, and has high toughness, which can meet the performance requirements of the hypereutectic Al-Mg2Si composite material in the fields of automobiles, communications, electronics, aerospace, etc. The performance that the hypereutectic Al-Mg2Si composite material in the present invention can achieve is specifically: in the gravity casting state, the tensile strength is 185-200MPa, the yield strength is 105-110MPa, and the elongation reaches 6-8%; in the T6 state, the tensile strength is 300-360MPa, the yield strength is 235-270MPa, and the elongation reaches 5-7%.

[0114] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A hypereutectic Al-Mg2Si composite material, characterized in that: It is composed of the following components in mass percentage: Mg 9.0-22.1%, Si 6.5-16.0%, Cu 0-0.8%, Fe 0.1-0.8%, Mn 0-0.4%, Be 0.002-0.005%, Sr 0.006-0.05%, RE 0.10-0.20%, trace impurities ≤ 0.15%, Al as the balance, Wherein, the mass ratio of Mg to Si is ≤1.6, and RE is selected from at least one of La and Ce; The hypereutectic Al-Mg2Si composite material contains Mg2Si.

2. The hypereutectic Al-Mg2Si composite material according to claim 1, characterized in that: Taking the total mass percentage of the hypereutectic Al-Mg2Si composite material as 100%, the mass percentage of the Mg2Si is greater than 13.9%.

3. The hypereutectic Al-Mg2Si composite material according to claim 1, characterized in that: When the mass percentage of Fe in the hypereutectic Al-Mg2Si composite material is 0.2-0.6%, the mass percentage of Mn is not 0.

4. The method for preparing the hypereutectic Al-Mg2Si composite material according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: melting part of the raw materials and performing the first refining, and then adding Al-Be alloy to obtain the first melt; S2: melting the first melt, Mg, optionally added Mn, and RE, and then performing a second refining to obtain a second melt; S3: melting the second melt and the Al-Sr-RE alloy, and then casting to obtain the hypereutectic Al-Mg2Si composite material.

5. The method for preparing the hypereutectic Al-Mg2Si composite material according to claim 4, characterized in that: The step S2 also includes the step of adding raw materials until the alloy composition is qualified; the step of adding raw materials until the alloy composition is qualified is located before and / or after the fusion step.

6. The method for preparing the hypereutectic Al-Mg2Si composite material according to claim 4, characterized in that: Taking the mass percentage of the Al-Sr-RE alloy as 100%, the total mass percentage of Sr and RE is 15-23%.

7. The method for preparing the hypereutectic Al-Mg2Si composite material according to claim 4, characterized in that: Taking the mass percentage of the first melt as 100%, the mass percentage of the RE is 0.06% to 0.18%; And / or, based on the mass percentage of the second melt being 100%, the mass percentage of the Al—Sr—RE alloy is 0.1% to 1.0%.

8. The method for preparing a hypereutectic Al-Mg2Si composite material according to claim 4, characterized in that: The first refining step is: using an inert gas as a carrier to introduce a halide salt refining agent for refining; And / or, the second refining step is: refining by introducing a sodium-free halide salt refining agent using an inert gas as a carrier.

9. The method for preparing a hypereutectic Al-Mg2Si composite material according to claim 4, characterized in that: The part of the raw materials includes at least one of Al-Si-Mg recycled aluminum material, Al-Si-Mg-Cu recycled aluminum material, Al-Mg-Si recycled aluminum material, and Al-Mg-Si-Cu recycled aluminum material.

10. Application of the hypereutectic Al-Mg2Si composite material according to any one of claims 1 to 3 and / or the method for preparing the hypereutectic Al-Mg2Si composite material according to any one of claims 4 to 9 in the automotive, communication, electronic or aerospace fields.

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